The present invention relates to a compact antenna used for a portable terminal, and to a producing method of the compact antenna.
FIG. 26 show an outline structure of a conventional compact antenna used for a portable terminal. An antenna 301 shown in FIG. 26A has a meander-shaped radiating section 301a, and the radiating section 301a is surrounded by a dielectric 301b. The radiating section 301a is continuously formed with a terminal 301c to be connected to a circuit board. Similarly, a compact antenna 302 shown in FIG. 26B has a helical-shaped radiating section 302a surrounded by a dielectric 302b. The radiating section 302a is continuously formed with a terminal 302c. 
To enhance the radiation efficiency of the antennas, it is necessary to enhance the electric conductivity of each of the radiating sections 301a and 302a as high as possible. That is, if the electric conductivity of each of the radiating sections 301a and 302a is low, a rate of electric power supplied to the radiating sections 301a and 302a which becomes thermal energy and is lost is increased. Therefore, it is preferable that the electric conductivity is as high as possible.
It is an object of this invention to provide a compact antenna capable of enhancing the radiation efficiency.
It is another object of this invention to provide a compact antenna capable of being mounted strongly to a circuit board, and to provide a producing method of the compact antenna.
According to one aspect of the invention, a compact antenna comprises an antenna conductor having a bent linear core, and a connection film which covers at least a portion of an outer surface of the core and which has higher electric conductivity than that of the core.
The connection film has a film thickness equal to or greater than a skin depth xcex4 specified by the following equation:
xcex4=(2/("sgr"xc2x7xcexcxc2x7xcfx89)),
Wherein "sgr" is electric conductivity of the conductor, xcexc is magnetic permeability and xcfx89 is angular frequency.
According to another aspect of the invention, a compact antenna having an antenna conductor comprises a radiating section for sending and receiving radio wave, and a terminal for connecting the radiating section and a circuit board, the terminal is coated with a connection film for enhancing soldering characteristic, and the radiating section is not formed with the connection film.
According to still another aspect of the invention, a producing method of a compact antenna comprises a stamping step in which an antenna conductor comprising a radiating section for sending and receiving radio wave and a terminal for connecting the radiating section to a circuit board is formed by stamping a metal plate, a coating step which coats the radiating section with dielectric, and a connection film forming step in which the connection film is selectively formed for the terminal using the dielectric as a mask.
Other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.